R. Dale Guthrie, a Fairbanks researcher, said radiocarbon dating of a tooth fossil shows mammoths still roamed St. Paul Island in the Bering Sea about 8,000 years ago, at least 3,000 years after widespread extinction of the species.

"This is the first one found in the New World," Guthrie said. "It was there because of very unique circumstances."

Woolly mammoths became extinct across the plains of Europe, Asia and North America at the end of the prehistoric period called Pleistocene, about 11,000 years ago. But some of the animals survived well into the next era, Holocene, after being stranded on St. Paul Island, Guthrie wrote in an article published Thursday in the science journal Nature.

Other cases of Holocene survival have been documented, including a specimen found on Wrangel Island in northern Russia that suggests extinction there occurred about 3,700 years ago.

But the St. Paul fossil represents the first known case in the Americas, according to Guthrie, a professor emeritus at the Institute of Arctic Biology at the University of Alaska Fairbanks. Older dated mammoth fossils are regularly found throughout Alaska and the Yukon Territory.

"This is an important find," said Paul Matheus, a researcher with UAF's Alaska Quaternary Center. "It's equivalent to finding a 50-million-year-old dinosaur, instead of a 65-million-year-old dinosaur. One find with the right date can change all of our ideas."

The St. Paul mammoths might have continued there for hundreds of years more until the island reached its present size of 36 square miles about 5,000 years ago, Guthrie said. St. Paul, which was created during the last major glacial meltdown 13,000 years ago, is part of the Pribilof Islands about 750 miles west of Anchorage.

"This was a very large island 13,000 years ago," Guthrie said. "As the water continued to come up, it became more and more restrictive until the mammoths just weren't able to make it."

The specimen - a fragment of a molar - differs significantly from mammoth fossils found throughout Alaska. It's smaller, suggesting the St. Paul mammoths began downsizing in response to a shrinking environment that was once a vast plain.

"I see it as an evolutionary change," Guthrie said.

Guthrie's study was part of a larger radiocarbon dating project that looked at extinct species, including mammoths from Alaska. Research included analyzing fossils stored at several museums, including the Smithsonian Institution's National Museum of Natural History in Washington, D.C. That's where Guthrie found the St. Paul fossil, which was excavated in 1964 from a northeast corner of the island.

Evidence that an isolated population of mammoths survived raises questions. For example, why did the St. Paul population survive while others perished on the mainland and neighboring islands?

Because widespread extinction coincided with the arrival of humans in the region, Guthrie speculates that people might have played a significant role. Other possible contributors include climate changes that altered the mammoths' feeding grounds and increasing competition from Holocene mammals such as bison and moose.

"Major changes in the world were occurring at this time," Guthrie said. "There was such a cataclysmic shift."